Formation Of Tridymite Research Articles

Utilization of copper slag in the fabrication of silica refractory: Characteristics and performance evaluation

AbstractIt is urgently necessary for environmental resource utilization of copper slag with incremental quantities of stacked copper slag. In this paper, copper slag has been used as mineralizer and raw material to prepare silica refractory. The effect of copper slag on phase composition, microstructure, mechanical, and load deformation performance has been investigated. The results indicate that the components of copper slag as mineralizer promote the formation of tridymite. Simultaneously, copper slag promotes the densification of silica refractory and glass phase increases due to the mineralizer and impurities in copper slag. The increased glass phase promotes the cold crushing strength and cold modulus of rupture for silica refractory, while the hot modulus of rupture slightly decreases by 1.5 MPa for 6 wt% copper slag. In addition, the load softening temperature and high‐temperature creep attains 1632.6°C and ‐5.5%, respectively. It is estimated that the potential application of silica refractory with copper slag on upper part of copper stove (low‐temperature and low‐load region) is acceptable in consideration of environmental utilization of solid waste.

Effects of nano-CaCO3 and nano-iron phosphate on microstructure and properties of SiO2 porous ceramics prepared by direct foaming

SiO2 porous ceramics are often used in industrial kilns for thermal insulation. Burning loss method is the main method for preparing SiO2 porous ceramics at present, but there are problems of environmental pollution and uneven pore distribution. Meanwhile, SiO2 is prone to cracking due to crystal-to-crystal transformations. In order to overcome above problems, in this study, nano-CaCO3 and nano-iron phosphate with high activity have been used to stabilize the crystal-to-crystal transformations of SiO2, and SiO2 porous ceramics have been prepared by simple and environmental direct foaming method. Results show that the addition of nano-CaCO3 and nano-iron phosphate can promote the formation of tridymite and densification of SiO2 porous ceramics, which can also increase their pore wall thickness and improve compressive strength. In addition, the compressive strength of SiO2 porous ceramics is proportional to their relative density, which is consistent with the Ashby’s theory. And their thermal conductivity is well matched with the universal model, indicating that SiO2 porous ceramics have complex pore structures. Comparing the effects of nano-CaCO3 and nano-iron phosphate on SiO2 porous ceramics, it is concluded that nano-CaCO3 as the mineralizer is better than nano-iron phosphate. This study enriches the fabrication technology of energy-saving and environmentally friendly SiO2 porous ceramics, which is of great significance to the practical production and application of SiO2 porous ceramics.

Sodium glass liquid from glass waste as a user-friendly hardener in structural geopolymer systems

Soluble alkali silicates, known as hardeners, play a vital role in the production of geopolymer binders. Currently, different industrial techniques are used to manufacture soluble alkali silicate from different glassy minerals on a large scale, where the major concerns are related to their reactivity as well as their ability to sustain user-friendliness criteria. This paper aims to maximise the use of glass waste (GW) in geopolymer technology through its combined utilisation as a friendly hardener product and a precursor powder in the production of structural geopolymer binders. Sodium glass liquids (SGLs) from GW were developed to encounter SiO2/Na2O molar ratio (MR) of 1.25 as the threshold level of user-friendliness for soluble silica. Various factors involved in the dissolution of silica were investigated using the Taguchi design of experiments and hierarchical analysis of variances (ANOVA). Optimum SGLs were considered to develop geopolymer binders derived from metakaolin (MK) and 0%, 25% and 50% of devitrified glass powder (DGW). Mixture combinations were algorithmically designed based on targeted chemical and physical ratios of SiO2/Al2O3, Na2O/SiO2, liquid/solid and MK/DGW. Mechanical strength and microstructural characteristics were evaluated on the developed geopolymer binders. Acid washing and tridymite formation significantly increases soluble silica content in SGLs. The chemical adjustment of geopolymers allowed the development of high strength binders of user-friendly hardener and 25% and 50% DGW precursor while reducing the commercial sodium silicate by up to 48%. The creation of Q2 as a new phase of silica species in user-friendly hardener and the formation of more silanol (Si–OH) groups from DGW compared to metakaolin were shown as the outcome of using SGL hardener and DGW precursor in geopolymer binders.

Formation of Tridymite and Evidence for a Hydrothermal History at Gale Crater, Mars

AbstractIn August 2015, the Curiosity Mars rover discovered tridymite, a high‐temperature silica polymorph, in Gale crater. The existing model for its occurrence suggests erosion and detrital sedimentation from silicic volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicic volcanic material. Using data from Curiosity, including chemical composition from the Alpha Particle X‐ray Spectrometer, mineralogy from the CheMin instrument, and evolved gas and isotopic analyses from the Sample Analysis at Mars instrument, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silica‐rich alteration halos which crosscut the stratigraphy. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification.

Evaluation of the tridymite formation as a technique for enhancing geopolymer binders based on glass waste

The low solubility of glass powder is one of the important elements hindering the large volume recycling of glass waste (GW) in structural geopolymer materials. The current study aims to investigate an enhancement process of GW to be reused in improved performance geopolymer binders. The method relies on the devitrification of GW powder through heat treatment at below and above the transition temperature of quartz in order to develop new phases of tridymite formation. The devitrified glass waste (DGW) was incorporated in optimized combinations with metakaolin using an algorithmic mixture design approach of pre-targeted ratios of SiO2/Al2O3, Na2O/SiO2 and liquid/solid. Mixtures of raw GW and metakaolin were used as control geopolymers. Mechanical strengths of the developed binders were assessed up to 90 days of ambient curing. In addition to the X-ray diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) used to characterize the formation of tridymite in DGW powder, comprehensive analysis, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and FTIR, was completed to inspect the microstructural change based on oxide ratios and DGW contents. Sustainability analysis was also performed to assess the energy consumption and CO2 emission of the produced geopolymer binders. The results indicated that the maximum tridymite formation occurred under 1-h heating at a temperature of 900 °C. The existence of higher tridymite content caused a significant increase in the compressive strengths of geopolymers made of 75% DGW compared to control mixtures with raw GW. The creation of more silanol (Si–OH) groups and generation of accelerated and greater degree of geopolymerization were shown as the outcomes of DGW in the geopolymer reaction process of binders.

Research in the Area of Preparing Materials Based on Fuzed Quartz HCBS. Part 10. Some Properties of Cristobalite-Containing Materials1

The effect of repeated nonisothermal heating to 1500°C on shrinkage and crystallization of quartz ceramic with added alkali (0.5% Na2O) and monolithic fuzed quartz is studied. Marked (up to 10%) tridymite formation is detected in specimens with added alkali and with a predominant cristobalite content. Some properties are provide for specimens after single-stage heating to 1500°C. Depending on additive content specimens have open porosity of 6 – 9% and ultimate strength in compression of 130 – 185 MPa.

The formation of silica high temperature polymorphs from quartz: Influence of grain size and mineralising agents

The formation of high-temperature silica polymorphs in presence of Na and K has been studied at various temperatures and soaking times, starting from quartzes of different grain size, ex situ as well as in situ. The results show that cristobalite and tridymite formation is strongly influenced by the nature and the amount of mineraliser added. In particular, K seems to discriminate more between the two structures, as it produces the largest observed amount of cristobalite. The disappearance of quartz can be controlled by the proper combination of mineraliser/temperature/time, which in turn control the amount and the type of polymorph formed, together with the amount of amorphous matter. Cristobalite is always the first to form, in agreement with the lower defect formation energy calculated by means of a periodic Linear Combination of Atomic Orbitals hybrid approach (Hartree–Fock and DFT), and tridymite follows, at its expenses. Bearing in mind that the interaction of Na and K with a complete ceramic mixture at high temperature is still largely unknown, this paper demonstrates that the high temperature silica polymorphs formation from quartz is easily controllable by means of the addition of known amount of mineralisers.

Microstructural Evolution in Clay‐Based Ceramics II: Ternary and Quaternary Mixtures of Clay, Flux, and Quartz Filler

The complex microstructural evolution in mixtures of kaolinite clay, quartz, nepheline syenite, and soda–lime–silica (SLS) glass has been revisited. Detailed descriptions of reactions leading to dense whiteware bodies backed by semi‐quantitative X‐ray diffraction analysis reveal that ternary mixtures containing nepheline syenite differ from those containing SLS glass, as new crystalline phases develop inside and at the interfaces among SLS glass particles and decomposed clay and quartz. In SLS glass‐fluxed mixtures, tridymite formation was hindered and cristobalite formed at ≥750°C followed by wollastonite at ≥800°C. Albite and plagioclase formed from interaction between clay and molten SLS glass above 800°C. Wollastonite was not present ≥1100°C, leaving only cristobalite in the surrounding regions. Quartz partially dissolves at temperatures ≥1000°C after interacting with molten SLS glass. In quaternary mixtures containing 6.25 wt% SLS glass and 17.25 wt% nepheline syenite fluxes, formation of types II and III secondary mullite was more pronounced than in the fully SLS glass‐fluxed mixture. The more fluid liquid from nepheline syenite enhances the growth kinetics of mullite. The body fired at the optimum firing temperature (1100°C) has a microstructure containing primary type I and secondary types II and III mullites, remnant cristobalite, plagioclase, and partially dissolved quartz embedded in the glassy phase. Providing a roadmap for microstructural design in clay‐based systems may have significant commercial impact in the emerging technology of use of waste materials in clay‐based ceramics.

Polymorphism of silica

A study of the stability relations of pure silica phases is described. It is shown that although cristobalite can be produced from pure quartz by heating it is not possible to produce tridymite in this fashion; a flux or mineralizer is required for tridymite formation and even in this case cristobalite is produced before any tridymite is observed. Thus it is concluded that the stability relations for the silica minerals proposed by Fenner are incorrect and that tridymite is not a stable phase in the pure silica system.

Kinetics of tridymite formation

Abstract The kinetics of tridymite formation has been studied. Colloidal silicas containing

Some features of the microstructure of a silaceous ceramic concrete

When a silaceous ceramic concrete is heat-treated, the particles of dispersed quartz binder degenerate according to the “dry” system:α-quartz→α-cristobalite, i. e., without the formation of tridymite.

Formation of tridymite and cristobalite from quartz in porcelain

Formation of tridymite and cristobalite from quartz in porcelain

Influence of Boric Oxide on Vitrification of Amorphous and Crystalline forms of Silica

Phase transformations of silica in mixtures containing boric oxide and three forms of silica, namely, amorphous silica, quartz and ordered cristobalite, were studied by the X-ray and DTA methods. With 5, 7.5 and 10 wt per cent of boric oxide, amorphous silica readily and completely vitrified at about 1480°C, 1300°C and 1040°C, respectively but not the crystalline forms, even after heating for periods upto 50 hours. The results suggest that with increasing boric oxide content, larger proportions of amorphous silica were directly converted to SiO2-B2O3 glass before any cristobalite could appear.Boric oxide accelerates the formation of tridymite from quartz and cristobalite, but does not permit conversion of quartz to cristobalite. At higher temperatures, quartz was probably transformed to an intermediate amorphous form and then to SiO2-B2O3 glass before any cristobalite could be formed. Starting with either ordered cristobalite or amorphous silica only a particular disordered form of cristobalite, showing α...

Conversion of Quartz to Tridymite

The conditions under which tridymite becomes a stable phase have been reinvestigated. When quartz was heated with 2% alkali oxide, tridymite formed directly at 872° to 898°C. with Na2O, at 883° to 902°C. with K2O, and above 1005°C. with Li2O. Cristobalite occurred as an intermediate phase above 893°C. with Li2O, above 898°C. with Na2O, and above 902°C. with K2O. When quartz plus sodium chloride was heated in vacuum, tridymite did not form but cristobalite started to appear at 1050°C. The results showed that the formation of tridymite can be strictly a solid‐state process. New schematic tentative diagrams for the high‐silica region of binary systems are suggested. Quartz and cristobalite are regarded as the only stable crystalline phases of pure silica. Tridymite is pictured as a binary incongruently melting phase.

Some Studies on Matrix in Silica Brick

In the first report, we have proposed “matrix brick” which is made of quartz flour through the 1600 hole/cm2 sieve mixed with abt. 5% of CaO. In mixing this “matrix” with varions amounts of coarer grains (400-1600 hole/cm2), we found that the sample cones containing less than 30% of “matrix” are more refractory, and therefore such bricks are good for use in open-hearth roof.In the second report, results of dilatometric experiments and microscopic observations of matrix bricks are given. There are two remarkable periods of mineral development during the sintering of matrix bricks; i.e.1000-1200°C cristobalite development1200-1400°C tridymite developmentThe formation of tridymite was detected byT1-inversson (α→β1 trid.) in samples fired at lower temperaturesT2-inversion (crist.→trid.) in samples fired at higher temperaturesBy comparing parmanent expansions at 1000°C in reheating the bricks, a minimum was found in samples fired at 900-1100°C, Milk of lime in green body gradully absorbs CO2 and is converted into CaCO3 at abt. 600°C, then it decomposes. At abt. 800-900°C, formation of calcium silicate was concluded from a marked shrinkage, and at abt. 1400°C it became visible under a microscope in forming ring-like shaped crystals. When fired at above 1400°C, calcium silicate diffused into the matrix, but when cooled, it recrystallized again.In the present (third) report, experimental results of parmanent expansion, porosity, apparent density and permeability are given.In the firing range of 1100°-1200°C, the apparent specific gravity of the matrix bricks has decreased from 2.60 to less than 2.40, but the porosity has also decreased and the crushing strength increased. Because there is no great change of porosity during firing, it is advisable to make quality control in green body. Increase of CaO content is good for crystal growth of Tridymite but rather decreases the it's amount, and makes expansion smaller.

Some Studies on Matrix in Silica Brick, (I)

In the first report, we have proposed “matrix brick” which is made of quartz flour through the 1600 hole/cm2 sieve mixed with abt. 5% of CaO. In mixing this “matrix” with varions amounts of coarer grains (400-1600 hole/cm2), we found that the sample cones containing less than 30% of “matrix” are more refractory, and therefore such bricks are good for use in open-hearth roof.In the second report, results of dilatometric experiments and microscopic observations of matrix bricks are given. There are two remarkable periods of mineral development during the sintering of matrix bricks; i.e.1000-1200°C cristobalite development1200-1400°C tridymite developmentThe formation of tridymite was detected byT1-inversson (α→β1 trid.) in samples fired at lower temperaturesT2-inversion (crist.→trid.) in samples fired at higher temperaturesBy comparing parmanent expansions at 1000°C in reheating the bricks, a minimum was found in samples fired at 900-1100°C, Milk of lime in green body gradully absorbs CO2 and is converted into CaCO3 at abt. 600°C, then it decomposes. At abt. 800-900°C, formation of calcium silicate was concluded from a marked shrinkage, and at abt. 1400°C it became visible under a microscope in forming ring-like shaped crystals. When fired at above 1400°C, calcium silicate diffused into the matrix, but when cooled, it recrystallized again.In the present (third) report, experimental results of parmanent expansion, porosity, apparent density and permeability are given.In the firing range of 1100°-1200°C, the apparent specific gravity of the matrix bricks has decreased from 2.60 to less than 2.40, but the porosity has also decreased and the crushing strength increased. Because there is no great change of porosity during firing, it is advisable to make quality control in green body. Increase of CaO content is good for crystal growth of Tridymite but rather decreases the it's amount, and makes expansion smaller.